Let’s take the board at move 13.
Left side you have 2 4x4 stones alone in the corners, nice. But white occupy the ideal extension in the middle and destroy the influence of these stones. Wrong.
On the right side white just took a huge corner on the top. In exchange you have a group a bit too far from the edge (5th line) with some life potential but not that much points. W is in the lower right corner.
Conclusion: you are already late in the balance of the game.
To see how to share a corner, you can check the joseki section (menu on the left)
Avoid to play on 5 line at the beginning too.